The present invention relates to an optical print head suitable for use as a light source in electrostatography (electrostatic copying) and the like, and to a driver IC for use in such an optical print head.
As disclosed in Japanese Utility Model Published No. H6-48887, in a light-emitting device (array) used in a conventional optical print head, for a plurality of light-emitting portions built as light-emitting diodes, separate electrodes are provided, one for each of the light-emitting portions, on the front surface of the device, and a common electrode, common to all the light-emitting portions, is provided on the back surface of the device. This makes it impossible to perform time-division driving within the device. Where time-division driving is impossible, it is inevitable to provide the same number of separate electrodes as the light-emitting portions. Consequently, as the light-emitting portions are formed with increasingly high density, the separate electrodes need to be formed with accordingly high density, and this makes it difficult to connect the device to a driver IC.
To solve this problem, Japanese Patent Application Laid-Open No. H6-163980 proposes a light-emitting device that permits time-division driving within the device. Specifically, a plurality of light-emitting portions formed on the light-emitting device are grouped into m groups. Moreover, m common electrodes are provided in such a way that each common electrode is connected to the light-emitting portions belonging to one group, and n separate electrodes are provided in such a way that each separate electrode is connected to m light-emitting portions belonging to different groups. Thus, the light-emitting device is provided with mxc3x97n light-emitting portions in total. In this light-emitting device, it is possible to select one among m common electrodes on a time-division basis, and this makes it possible to reduce the number of separate electrodes to 1/m of the number conventionally required. This makes it easy to connect the device to a driver IC.
A light-emitting device like this can be driven on a time-division basis by the use of a in, driver IC like those used conventionally. However, in that case, it is necessary to provide separately a driving circuit for selecting the common electrodes of the light-emitting device on a time-division basis. For this reason, efforts have been made to develop a driver IC designed for general purpose use and in addition suitable for time-division driving.
With the aforementioned points in mind, the applicant of the present invention once proposed a driver IC in Japanese Patent Application Laid-Open No. H10-2226102. However, the arrangement proposed in this publication requires an additional process of altering the order of data input to suit time-division driving, and thus requires more complicated data processing.
Moreover, in conventional arrangements, as the number of groups increases, the number of control signal lines for selecting them accordingly increases. This inevitably increases the number of terminals of a driver IC.
An object of the present invention is to provide a driver IC suitable to drive a light-emitting device ready for time-division driving.
Another object of the present invention is to reduce the number of terminals of a driver IC designed to drive a light-emitting device on a group-by-group basis.
To achieve the above objects, according to one aspect of the present invention, in a driver IC having a first driver section for outputting driving signals via n output terminals and a second driver section for selectively switching one of m selection terminals (where mxe2x89xa73) to a predetermined potential, wherein the first driver section includes a control circuit for designating the destinations to which the second driver is to supply the driving signals, and the control circuit designates the destinations to which to supply the driving signals on the basis of control signals that are fed thereto from outside by way of a number of signal lines fewer than m.
According to another aspect of the present invention, in a driver IC having a first driver section for outputting driving signals via n output terminals and a second driver section for selectively switching one of m selection terminals to a predetermined potential, the first driver section is composed of a data signal storage circuit for storing at least nxc3x97m data signals fed thereto sequentially, a data selection circuit for selecting and extracting, in batches of n data signals, the data signals stored in the data signal storage circuit, and a drive circuit for outputting the driving signals on the basis of the data signals selected by the data selection circuit.
According to another aspect of the present invention, in an optical print head composed of a light-emitting device, having n separate electrodes each connected to first electrodes of m light-emitting diodes (where mxe2x89xa73) and m common electrodes connected individually to the second electrodes of the m light-emitting diodes, and a driver IC, having n output terminals connected individually to the separate electrodes, a first driver section for outputting the driving signals via the output terminals, m selection terminals connected individually to the common electrodes, and a second driver section for selectively switching one of the selection terminals to a predetermined potential, wherein the first driver section includes a control circuit for designating the destinations to which the second driver section is to supply the driving signals, and the control circuit designates the destinations to which to supply the driving signals on the basis of control signals that are fed thereto from outside by way of a number of signal lines fewer than m.
According to another aspect of the present invention, in an optical print head composed of a light-emitting device, having n separate electrodes each connected to first electrodes of m light-emitting diodes (where mxe2x89xa73) and m common electrodes connected individually to the second electrodes of the m light-emitting diodes, and a driver IC, having n output terminals connected individually to the separate electrodes, a first driver section for outputting the driving signals via the output terminals, m selection terminals connected individually to the common electrodes, and a second driver section for selectively switching one of the selection terminals to a predetermined potential, the first driver section is composed of a data signal storage circuit for storing at least nxc3x97m data signals fed thereto sequentially, a data selection circuit for selecting and extracting, in batches of n data signals, the data signals stored in the data signal storage circuit, and a drive circuit for outputting the driving signals on the basis of the data signals selected by the data selection circuit.